Method of making felt



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United States Patent Ofifice 3,060,548 Patented Oct. 30, 1962 Bethesda, Md, assignors to Western Felt Works, Chicago, Ill.

No Drawing. Filed Sept. 16, 1959, Ser. No. 840,245 12 Claims. (Cl. 28-723) This invention relates to a method of making felt in which the expensive and time-consuming hardening operation is replaced by a comparatively simple and inexpensive bonding operation. More specifically, this invention relates to a method for making felt in which a bonding agent is added to a batt of fibers and the fibers are bonded together under heat and pressure, after which the bonded batt is fulled in either a kicker mill, a hammer mill or a rotary fulling mill.

The term felt as used herein is intended to designate a fabric which is built up by the interlocking of fibers induced by a combination of mechanical working, chemical action and heat, Without spinning, weaving or knitting. It contains wool and in addition it may contain animal, vegetable or synthetic fibers of the type normally used in making felt. Felt as defined herein is to be distinguished from other materials which have a felt-like appearance but in which the fibers are held together solely by bonding agents, weaving or other means not involving an interlockiug of fibers induced by mechanical working.

Felt which is formed in a sheet and subsequently cut to the desired shape is termed pressed felt while the term hat felt is used to denote felt which is made individually on conical forms so as to more nearly approach the shape of the finished hat at each stage of manufacture. The method of this invention can be used advantageously in themaking of both pressed and hat felts. 1

True felt must contain some vWool (or'certain animal fibers) because during the fulling operation (to be described hereinafter) it is the wool fiberszthat are induced to migrate or interlock so as to form afirm fabric. The minimum amount of wool or 'feltable hair fibers necessary to produce a satisfactory felt product depends upon the type of Wool used and upon the nature of the additional fibers that are added thereto. imum of about 20% of good feltable wool is required to produce a satisfactory felt product.

With the conventional method of making felt as here-' tofore known the first main step is to form a carded batt of loose fibers about 90 inches-wide. th1ckness of the batt depends upon the desired weight and thickness of the finished felt. The batt of loose fibers.

is rolled up on a pole. It is weak and easily distorted and thus difiicult to handle. The batt of fibers is then subjected to a hardening operation the main purpose of which is to partially felt the fibers in the batt so that the batt will hold together and can be easily handled during subsequent operations. The hardened batt is then fulled i.e. subjected to a vigorous mechanical action, in either a kicker mill, a hammer mill or a' rotary fulling mill.

The hardening operation referred to above is an expensive and-time-consuining batch process. It consists in placing a batt of loose fibers which is approximately 50 The batt is moistenedclosed and vibrated violently in a reciprocating motion The combination of for approximately 1 to 2 minutes. moisture, heat and mechanical action causes a partial In general, a min-' The weight and z migration or interlocking of the individual fibers so as to form a hardened batt which can be handled without excessive distortion.

It will be understood that-hardening is abatch operation and only about 1 to 3 yards of the length of batt can be hardened at one time. While it is possible to harden as many as four thin batts simultaneously by placing a woven hardener cloth between them, yet even when this is done the hardening operation is a slow, intermittent and expensive operation. It is usually necessaryto harden both sides of a batt which further increases the time and expense involved. Also, considerable mechanical energy is required to vibrate the heavy metal plates and considerable maintenance and repair work is required on the hardening machines. I

As previously stated, the present invention relates to a method of making felt whereby the above hardening operation is eliminated and replaced by a continuous bonding operation.

The use of a bonding operation in the present invention as one step in the production of felt is to be distinguished from the use of bonding as a means of producing bonded fabrics which have an entirely different construction and generally poorer physical properties than that of felt. For

example, Reed Patent No. 2,277,049'discloses a method of making a bonded fabric which consists in carding a web comprising non-binder textile fibers (usually cotton). and

thermoplastic binder fibers and applying heat and pres-' there is no migration or interlocking of the fibers as in;

felt and it is only the bonding agent that holds the fabric together. They need not contain any wool and in fact they seldom do. Thus, in this type of bonded fabric the individual fibers are held together only at the points where they cross the binder fibers whereas'with felt the fibers are thoroughly migrated so as to be throughout their length..-

While bonded fabrics are inexpensive to produce and have varied commercial uses sucha's in tea bags, disposable diapers and towels, garment interlinings, luggage lining,- etc. yet they do not have the properties'of felt and are clearly not asubstitute therefor. I

According'to the present invention a bonding operation is substituted for the conventional hardening operation 1; and lessexpensive than the felt-making processes heretoof the felt-making process and the bonded'batt of fibers is fulled, i.e. subjected to vigorous mechanical action in a hammer mill or the like. The product of this invention is not a bonded fabric but a true felt and in fact the bonding agent can be dissolved out of the felt after fulling by means of a suitable solvent if desired.

One object of this invention is, therefore, to provide a method of making felt which is less time-consuming fore known.

Another object of this invention is'to provide a method of making felt in which the intermittent hardening operation is eliminated. Y

A further object of this invention is to provide a method of making felt which includes a continuous bonding operation as one step thereof.

A still further object of this invention is to provide a; method of making felt whereby a bonding agent is usedv (I to hold the batt of fibers together until the" subsequent locked together" fulling operation is completed after which the bonding agent can be removed from the final product.

Other objects and advantages of this invention will be apparent from the following description of a preferred embodiment thereof:

In making felt according to the present invention, fibers of the proper weight, width and length for the particular felt style desired are formed into a batt by one of the usual methods such as carding, garnetting or air-blowing. The batt of fibers can be formed with either all straight or straight and cross webs. As previously described, according to our method the batt-forming process is followed by a bonding operation.

The bonding agent can be either a thermoplastic fiber, a resin (in either solid or liquid form), a rubber or other chemical regularly used in bonding fibers together.

While any thermoplastic fiber can be used, yet in order to prevent heat damage to the wool fibers it is preferable to use a thermoplastic fiber that melts at a temperature below about 400 degrees F. Some examples of such fibers are plasticized cellulose acetate, Vinyon, Dynel, polyethylene, Saran, cellulose acetate, polyvinyl chloride fiber and Dacron of the type having a low melting temperature. When a thermoplastic fiber is used as the bonding agent it should be intimately mixed with the main fibers of the batt during the above batt-making process.

It is preferable to use as fine a thermoplastic fiber as is practical to blend and mix with the wool being used to make the felt. When thin fibers are used it is possible to employ a greater number of fibers in a given weight of binder and thus achieve a greater number of bonding areas in the batt. Generally, a binder fiber of about 3 denier will give very satisfactory results (denier is the weight in grams of a fiber 9000 meters in length).

The staple length of the thermoplastic fiber should preferably be as long as is practical to use with the particular type of carding machine being employed to form the batt without causing excessive breakage of the fiber. With woolen cards this is generally about 3 inches and with cotton cards (which can be used to card wool) this length is about 1 /2 to 2 inches. However, thermoplastic fibers considerably longer or shorter than these can be used with quite satisfactory results. A fairly long binder fiber is desirable because as the fiber melts during the bonding operation (to be described hereinafter) it shrinks somewhat in length and a short thermoplastic fiber will thus result in a small head which will bond together comparatively few wool fibers. We have found that thermoplastic fibers are particularly useful as the bonding agent in our process.

Any thermoplastic resin solid or powder that will fuse or melt at a temperature below approximately 400 degrees F. can also be used as a bonding agent. Furthermore, any thermoplastic resin liquid having a melting temperature below about 400 degrees -F. can be sprayed onto the fiber batt and used as the bonding agent. In such a case the liquid resin can be applied to the batts either from an aqueous emulsion or from an organic solvent solution, e.g. polyvinyl chloride resin dissolved in toluene. However, because of the toxicity and flammability of the organic solvent systems the aqueous emulsions of thermoplastic resin are preferred where a liquid binder is to be used.

In addition, many thermosetting resin solutions or emulsions and synthetic rubber dispersions in water (latices) can be used as the bonding agent. Some specific examples of bonding agents other than thermoplastic fibers that may be used are polyvinyl acetate, polyvinyl chloride, acrylic resins, styrene resins, viscose dope and natural and synthetic rubbers. It should be understood that there are a great many chemicals too numerous to mention specifically which are known to be usable for bonding fibers together and which can be used in the present invention either in solid or liquid form as the bonding agent.

The method of applying the bonding agent to the fibers and the time at which it is applied, i.e. whether it is applied during the formation of the batt or subsequent thereto, depend upon the particular type of agent used. Consequently our method of making felt is not limited to any one particular procedure for adding the bonding agent. A thermoplastic fiber bonding agent can be intimately mixed with the wool fibers during the carding or batt-forming operation without the need of special mill equipment. A resin-solid bonding agent can be mixed with the fibers at the cards although there is a risk of losing some of the resin during carding and other processing which occur before the batt is actually bonded by application of heat and pressure as described hereinafter. A solid or liquid resin binder can be applied to individual card webs as the batt is being formed or to the batt itself. However, the application of a solid or liquid chemical binder to card webs or to the finished batt by spraying or by shaking through a wire screen does not generally give as intimate a mixture of the binder with the wool fibers as can be obtained when fiber binders are used.

Uniform mixing of the binder with the wool fibers in the batt is important in order ot obtain uniform bonding. In our method the bonding operation is followed by a fulling operation and we have found that in order to achieve uniform felting during the fulling operation it is essential to provide a uniformly bonded batt. A chemical liquid bonding agent can be intimately applied to the wool fibers by impregnating the batt with the liquid but in such a case the batt should be dried before it is subjected to the subsequent fulling operation.

With respect to the amount of bonding agent that should be used in the process of this invention, we have found that an amount between approximately 5% and 25% of thermoplastic fiber should preferably be used (percentages of bonding agent are based upon the total weight of the batt). Since in our method for making felt the bonding operation is only an intermediate step in the entire process it is important to regulate the amount of bonding agent so as to produce a bonded batt which has properties suitable for the subsequent fulling operation where the batt is subjected to vigorous mechanical action.

Thus it has been found that unless at least approximately 5% of thermoplastic fiber is used the resulting batt will be poorly bonded and will not hold together so that it can be pulled over machine rolls, folded in a truck, padded with a fulling solution and manually handled at the fulling mill without tearing or pulling apart. Also, it should be noted that during the fulling operation mechanical work is performed upon the bonded batt in order to induce the wool fibers to migrate and become interlocked in a natural, self-tightening mat and we have found that if more than approximately 25% of thermoplastic fibers are used in the bonding operation the bonding agent will retard the migration of the wool fibers.

Of course, the optimum amount of bonding agent depends upon the type of binder used, the manner of mixing the binder with the fibers, the temperature and pressure of the calender rolls which are employed during the bonding operation and the speed of travel of the batt through the calender. It is desirable to use a minimum amount of bonding agent for reasons of economy and to ensure good felting during the fulling operation and we have found that optimum results are obtained when 10% to 15% of a thermoplastic fiber of fine denier and long staple length is blended with to of wool material or wool mixed with other fibers normally used to make felt. If a chemical bonding agent (rubber or resin solids applied in either the solid or liquid state) is used the amount should be maintained between about 2% and 25%.

Once the bonding agent has been added in one of the ways described above, heat and pressure are applied to, the batt to bind the fibers together. While any machine by which heat and pressure can be applied to the batt may be employed it is preferable to use calender rolls so as to render the bonding operation a continuous one. If a flatbed hydraulic press is used for bonding the operation is intermittent and for that reason less desirable. When a resin or rubber bonding agent is used it is possible to bond the fibers of the batt byapplication of heat alone. However, we have found that in our process where the bonded batt is subjected to a fulling operation to produce a firm felt material it is preferable to simultaneously apply heat and pressure during bonding regardless of the bonding agent being employed. It will be understood that in the making of hat felt the material is made on conical forms and thus theabove-mentioned methods for applying heat and pressure would not be suitable. However, various other means for applying heat and pressure to the fibers while they are positioned on the conical forms will readily occur to those in the trade.

Where the bonding agent is a thermoplastic resin liquid which is sprayed onto the fiber b'att the calender roll bonding can be carried out on the resin treated batt in either the moist state or in the dry state. Where thermosetting resin solutions or emulsions or synthetic rubber dispersions in water are used as the bonding agent the batt of fibers which is sprayed with these agents should be mechanically bonded under heat and pressure in the Wet or damp state and the batt should be dried and cured either during the calendering operation or by a subsequent drying operation.

The bonding conditions of roll temperature, pressure, distance between rolls and speed of travel of the butt depend upon the weight and thickness of the batt to be bonded as well as the type and percentage of the bonding agent and the diameter of the calender rolls. Without any intent to limit the process of this invention, it may be stated that we have obtained especially satisfactory bonding by using two 18" diameter metal-to-metal rolls which were heated to a temperature between approximately 350 degrees F. and 400 degrees F. and subjected to a pressure of from about 100 to 200 pounds per linear inch of roll. The speed of travel of the batt between the rolls should be maintained between about 5 and 50 yards per minute. Also it has been found that if the final belt product resulting from the fulling operation is to be of optimum quality the 'batt should be compressed in thickness by about 75% to 95%, based upon the original thickness of the batt, during the bonding operation.

The application of heat and pressure as described above causes the thermoplastic fiber (or resin) to fuse and melt so *as to lock or bond the wool fibers together at the places in the batt where the bonding agent is present.

It will now be understood that by the bonding opera- 1 tion the fiber batt is reduced in thickness and the fibers are held together by a partial felting or migration of the fibers. In the bonding process the batt is reduced to the desired thickness and the fibers are held together by the bonding agent which is activated by heat and pressure from the calendar rolls. It should be noted, however, that partial felting by hardening can be quite non-uniform due to over-lapping of places on the batts by the platents, by variations in moisture content of the batt and by the sticking of the fibers to the apron. The bonding process gives batts with smooth uniform surfaces which are uniform in both thickness and degree of bonding and more uniform felting during the falling operation can be achieved with such baits. 7

After the batt has been properly bonded it is subjected to the fulling operation. Prior to the actualfulling the batt is impregnated with an aqueous fulling agent. The aqueous solution can be either acidic, neutral or alkaline and it can" contain various surface active agents such as wetting agents, detergents, soap, softening agents, etc. which are referred to as falling assistants. For acid fullsolution. Soap solutions used for fulling contain from about 0.5% to 2% by weight of solution of various types V of soaps such as tall oil soap, sodium oleate or mixtures of soap and synthetic detergent. Also, synthetic detergent solutions alone may be used as fulling assistants;

The actual fulling operation consists in vigorously working the material in a kicker mill, a hammer mill or a rotary fulling mill. As previously described, this operation causes the wool fibers to migrate and become interlocked into a natural, self-tightening mat. It is not be: lieved that the fulling operation need be furtherdescribed in detail since this operation is well understood in the trade.

Subsequent to fulling there are various wet and dry finishing operations that can be carried out on the felt product. For example, the fulled felt may be neutralized and then scoured in a solution containing /2% sodium tripolyphosphate and /z% Triton X-lO'O a Rohm and Haas Company non-ionic type product designated alkyl-- 1 'arylpolyether alcohol) or other alkalies and synthetic detergent-s or soap. It may then be rinsed in water and dyed and/0r chemically treated with a mothproofing agent, etc, after which it is dried and finally dry-finished. N

If the felt is not to be dyed or chemically treated after neutralizing, scouring and rinsing it is dried and then finished by singeing, shearing or sanding and pressing;

However, here again operations such as these are the same as are normally used in conventional felt-making processes and a detailed description of them is not deemed essential in describing the presentinvention.

It will now be understood that while the method of this invention includes a bonding operation the felt product produced by said method is standard felt and is wholly different from a mere bonded fabric such as is produced by the process described in Reed Patent 2,277,049. Thus, while a bonding agent is needed to hold a bonded fabric together, yet with felt produced as described herein the bonding agent acn be removed from the final product." Normally this would be done only when a 100% Woolf felt is desired since We have found that the presence of the bonding agent does not injuriosuly affect the proper-f For example, if the felt product is 1 ties of the felt. V composed entirely of wool and a plasticized cellulose acetate binder fiber, then by removal of the cellulose acetate a 100% wool product can be obtained.

Any solvent which will dissolve the bonding agent" without damaging the wool fibers can be used to remove said agent.

ride and Vinyon.

A plasticized cellulose acetate binder can also be re Generally, after, felt is fulled with a sulfuric acid solution it is neutralized i" with an alkaline solution (e.g. ammonia or sodium car!" bonate) and then Washed and water rinsed. If'after fulling with sulfuric acid, at whichtime there is, about 5% of sulfuric acid by weight in the felt, the felt is not neutralized but rather is dried and then heatedfor about; 3 minutes at 300 degrees F., then the plasticized cellulose acetate will carbonize, i.e. char or turn to carbon, andjsuch' j moved from the felt by carbonizing.

decomposed material can be washed out of the felt.

The method of this invention has been described above in conjunction with the making of felt from a single batt formed from a single carded fiber web' or the like. 1 As thus described, our method would generally beusedjj, to makefelt having a final thickness of. 0.2.5 inchor less. 1 Normally,'thick felts are made from a plurality of batts which are placed on top of one another at the" Acetone wil dissolve cellulose acetate, polyg vinyl acetate, Vinyon and Dynel; alcohols will dissolve polyvinyl butyral binders and certain types of nylon; calcium chloride in methanol willdissolve some types of nylon; and tetrahydrofurane will dissolve polyvinyl chlo- 1 hardening machine because, while a single batt having the weight and thickness necessary to produce a thick felt can be formed, it cannot conveniently be transported to the hardener. When thick felts formed from a plurality of batts are made according to our process as previously described, they will have a low split strength (the split strength is a measure of the force required to pull or tear the felt apart in the thickness direction) and in some cases the batt may even tend to fall apart during fulling.

We have found, however, that our method can be used to produce high quality thick felts from a single batt composed of a plurality of fiber webs if a needling operation is performed during the batt-forming process. In other words, a plurality of carded fiber webs or the like are formed and arranged one upon the other and said Webs are needled during the batt-forming process by means of a standard needle punch machine so as to reduce the thickness of the Webs and lock them together into a single thick batt.

We have further found that a needled batt produced as described above can be felted in a fulling operation without any bonding so as to produce a high quality thick felt. When desired, a needled batt can also be bonded as previously described and, as in the making of thinner felts, somewhat more satisfactory results can be obtained when the binder is applied in fiber form to the batt prior to carding and needling.

It will now be seen that we have developed a new method of making felt which eliminates the conventional hardening operation and instead employs a calender bonding operation which involves lower production costs, less labor costs and less maintenance costs than hardening.

This method can, of course, be applied in various ways and the present description should, therefore, be regarded as disclosing only an illustrative embodiment of the invention from which no unnecessary limitations should be implied.

We claim:

1. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in forming an unfelted batt of fibers composed at least in part of wool fibers; adding a bonding agent to said unfelted batt; applying heat and pressure to said unfelted batt by calendering said batt in a continuous bonding operation so as to bond together the fibers of said batt and reduce the thickness thereof; and subjecting the unfelted, bonded batt to a fulling operation so as to produce a fulled felt therefrom.

2. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in forming an unfelted batt of fibers composed at least in part of wool fibers; adding a bonding agent to said unfelted batt; applying heat and pressure to said unfelted batt by calendering said batt in a continuous bonding operation so as to bond together the fibers of said batt and reduce the thickness of said batt by approximately 75% to 95% based upon the original thickness thereof; applying an aqueous fulling agent to the unfelted bonded batt; and subjecting said unfelted, bonded batt to a fulling operation so as to produce a fulled felt therefrom.

3. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in forming an unfelted batt of fibers composed at least in part of wool fibers and containing between approximately and 25% of thermoplastic binder fibers; applying heat and pressure to said unfelted batt by calendering said batt in a continuous bonding operation so as to bond together the fibers of said batt and reduce the thickness thereof; applying an aqueous fulling agent to the unfelted bonded batt; and subjecting said unfelted, bonded batt to a fulling operation so as to produce a fulled felt therefrom.

4. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in forming an unfelted batt of fibers composed at least in part of wool fibers; adding to said unfelted batt between approximately 2% and 25% of a chemical bonding agent; applying heat and pressure to said unfelted batt by calendering said batt in a continuous bonding operation so as to bond together the fibers of said batt and reduce the thickness thereof; applying an aqueous fulling agent to the unfelted bonded batt; and subjecting said unfelted, bonded batt to a fulling operation so as to produce a fulled felt therefrom.

5. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in forming an unfelted batt composed substantially entirely of wool fibers; adding a bonding agent to said unfelted batt; applying heat and pressure to said unfelted batt by calendering said batt in a continuous bonding operation so as to bond together the fibers of said batt and reduce the thickness thereof; subjecting the unfelted, bonded batt to a fulling operation so as to produce a fulled felt therefrom; and removing said bonding agent from said fulled felt.

6. A method of making thick felts having a final thickness greater than approximately 0.25 inch from a single batt composed of multiple unfelted fiber webs which consists in forming a plurality of fiber webs each of which is composed at least in part of wool fibers; adding a bonding agent to said unfelted fiber webs; arranging said webs one upon the other and needling the batt while it is being formed so as to reduce the thickness of said webs and lock them together into a single thick batt; applying heat and pressure to said thick batt by calendering said batt in a continuous bonding operation so as to bond together the fibers thereof; applying an aqueous fulling agent to the bonded batt; and fulling said bonded batt so as to produce a fulled felt therefrom.

7. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in forming an unfelted batt of fibers composed at least in part of wool fibers and containing between approximately 10% and 15% of thermoplastic binder fibers of the type having a melting point below approximately 400 degrees F.; applying heat and pressure to said unfelted batt by calendering said batt in a continuous bonding operation so as to bond together the fibers of said batt and reduce the thickness of said batt by approximately 75% to based upon the original thickness thereof; applying an aqueous fulling agent to the unfelted bonded batt; and subjecting said unfelted, bonded batt to a fulling operation so as to produce a fulled felt therefrom.

8. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in preparing a batt composed of feltable fibers, including wool fibers, and a bonding agent, subjecting said batt to a continuous bonding operation by application thereto of heat and pressure to bond the fibers together and reduce the thickness of the batt before any felting operation is performed thereon, and thereafter subjecting the bonded and compressed but otherwise unhardened batt to fulling as the sole felting operation thereon to produce the felt in sheet form.

9. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in preparing in continuous web form a batt composed of feltable fibers, including wool fibers, and a bonding agent, running the web through continuouslyoperating, heated, pressure-applying rollers to bond the fibers thereof together and reduce, the thickness of the lbatt web before any felting operation is performed thereon, and thereafter fulling the bonded and compressed but otherwise unhardened batt web to convert the same into felt in continuous sheet form.

10. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in preparing in continuous web form a batt composed of feltable fibers, including not less than about 20% of wool fibers, and a bonding agent in such an amount that it will comprise not less than about 2% and not more than about 25% of the batt when the latter is bonded, subjecting said batt web to a continuous bonding operation by running it through continuously-operating, heated, pressure-applying rollers to bond the fibers together and reduce the thickness of the batt web by about 75% to about 95%, before any felting operation is performed thereon, thereafter impregnating the batt web with an aqueous fulling agent and subjecting it to fulling as the sole felting operation thereon to convert the same into felt in continuous sheet form.

11. A continuous method of making felt by bonding and subsequent fulling without vibration hardening which consists in preparing in continuous web form a batt composed of feltable fibers, including not less than about 20% of wool fibers and between about 5% and about 25% of thermoplastic binder fibers, subjecting said batt to a continuous bonding operation by running it through continuously-operating, heated, pressure-applying rollers to bond the fibers together and reduce the thickness of the batt web by about 75% to about 95%, before any felting operation is performed thereon, thereafter impregnating the batt web with an aqueous fulling agent and subjecting it to fulling as the sole felting operation thereon to convert the same into felt in continuous sheet form. to

12. A method of making felt by bond-ing and subsequent fulling without vibration hardening which consists in preparing a batt composed of feltable fibers, including wool fibers, and a bonding agent in such an amount that it will comprise not less than about 2% and not more than about of the batt when the latter is bonded, subjecting said batt to a bonding operation by application thereto of heat and pressure to bond the fibers together and reduce the thickness of the batt before any felting operation is performed thereon, and thereafter subjecting the bonded and compressed but otherwise unhardened batt to fulling as the sole felting operation thereon to thereby felt the same.

References Cited in the file of this patent UNITED STATES PATENTS 2,156,455 Kleine et al. May 2, 1939 2,181,043 Boeddinghaus Nov. 21, 1939 2,277,049 Reed Mar. 24, 1942 FOREIGN PATENTS 1,789 Great Britain of 1907 

1. A CONTINUOUS METHOD OF MAKING FELT BY BONDING AND SUBSEQUENT FULLING WITHOUT VIBRATION HARDENING WHICH CONSISTS IN FORMING AN UNFELTED BATT OF FIBERS COMPOSED AT LEAST IN PART OF WOOL FIBERS; ADDING A BONDING AGENT TO SAID UNFELTED BATT; APPLYING HEAT AND PRESSURE TO SAID UNFELTED BATT BY CALENDERING SAID BATT IN A CONTINUOUS BONDING OPERATION SO AS TO BOND TOGETHER THE FIBERS OF SAID BATT AND REDUCE THE THICKNESS THEREOF; AND SUBJECTING THE UNFELTED, BONDED BATT TO A FULLING OPERATION SO AS TO PRODUCE A FULLED FELT THEREFROM. 